Forkhead box P3 regulates ARHGAP15 expression and affects migration of glioma cells through the Rac1 signaling pathway.

Forkhead box P3 (FOXP3) plays a crucial role in the development and function of regulatory T cells and was recently identified as a tumor suppressor in different cancer types. Forkhead box P3 is expressed in normal brain tissues, but is strongly downregulated or absent in glioblastomas. In order to understand the FOXP3 adjustment mechanisms in glioma cells, we performed a DNA microarray in U87 cells overexpressing FOXP3 and validated the differences using quantitative real-time PCR, Western blot analysis, and immunohistochemistry in vitro and in vivo. We found that FOXP3 can regulate the expression of ARHGAP15. Expression of FOXP3 was also correlated with ARHGAP15 in glioma samples. Overexpression of FOXP3 inhibited glioma cell migration through ARHGAP15 upregulation and Rac1 inactivation. Silencing of FOXP3 promoted migration through ARHGAP15 downregulation and Rac1 activation. ARHGAP15, a GTPase-activating protein for Rac1, inhibits small GTPase signaling in a dual negative manner. We found that there is a correlation between expression of ARHGAP15 and glioma level. The small GTPase Rac1 plays an important role in cell migration. In addition, we found that FOXP3 regulates expression of epithelial-mesenchymal transition markers E-cadherin and N-cadherin, which is important given that epithelial-mesenchymal transition is critically involved in tumor spreading and dissemination. Thus, FOXP3 or ARHGAP15 may serve as a new molecular target for antimetastatic therapies in treating glioma.

MiR-7-5p is frequently downregulated in glioblastoma microvasculature and inhibits vascular endothelial cell proliferation by targeting RAF1.

The aberrant expression of microRNAs (miRNAs) is always associated with tumor development and progression. Microvascular proliferation is one of the unique pathologic features of glioblastoma (GBM) . In this study, the microvasculature from GBM or normal brain tissue derived from neurosurgeries was purified and total RNA was isolated from purified microvasculature. The difference of miRNA expression profiles between glioblastoma microvasculature and normal brain capillaries was investigated. It was found that miR-7-5p in GBM microvessels was significantly reduced compared with that in normal brain capillaries. In the in vitro experiments, overexpression of miR-7-5p significantly inhibited human umbilical vein endothelial cell proliferation. Forced expression of miR-7-5p in human umbilical vein endothelial cells in vitro significantly reduced the protein level of RAF1 and repressed the activity of the luciferase, a reporter vector carrying the 3'-untranslated region of RAF1. These findings indicate that RAF1 is one of the miR-7-5p target genes. Furthermore, a significant inverse correlation between miR-7-5p expression and RAF1 protein level in GBM microvasculature was found. These data suggest that miR-7-5p functions as a tumor suppressor gene to regulate GBM microvascular endothelial cell proliferation potentially by targeting the RAF1 oncogene, implicating an important role for miR-7-5p in the pathogenesis of GBM. It may serve as a guide for the antitumor angiogenesis drug development.

Aging-related gene signature regulated by Nlrp3 predicts glioma progression.

Aging is the strongest risk factor for glioma development, suggesting that molecular crosstalks between aging and tumorigenesis exist in many cellular pathways. Recently, Nlrp3 inflammasome have been shown to modulate several major cellular pathways such as inflammation and cell death and have been demonstrated to be an upstream target that controlled the process of brain aging. We proposed Nlrp3 inflammasome may serve as a possible molecular link between aging and glioma progression. In this study, we generated a aging-related gene signature that regulated by Nlrp3 in mouse hippocampus and demonstrated that this gene signature can distinguish subsets of glioma samples and predicts clinical outcome in radiotherapy-treated patients. In addition, using U87 and GL261 xenograft mouse glioblastoma model, we found that Nlrp3 inflammasome contributed to radiotherapy resistance in glioma. Ionizing radiation can induce Nlrp3 inflammasome expression; Nlrp3 inhibition reduced tumor growth and prolonged the survival of mouse following IR treatment; Nlrp3 inhibition reduced number of senescent cells induced by IR. These results above suggest that Nlrp3 inflammasome is an important molecular link between brain aging and glioma progression; the Nlrp3 gene signature may serve as a predictive biomarker for glioma patients.

X-ray irradiation accelerates senescence in hippocampal neural stem/progenitor cells via caspase-1 activation.

Despite the effectiveness in controlling the progression of brain tumors, cranial irradiation often causes neuropsychological deficits in cancer survivors. Inflammation is considered a major cause of tissue injury from irradiation. The caspase-1 activation complexes (inflammasomes) can facilitate caspase-1 and IL-1ß processing, which amplifies the inflammatory response. In the present study we examined whether caspase-1 activation contributes to irradiation-induced damage to neural stem and progenitor cells (NSPCs). We found that X-ray irradiation induced activation of caspase-1 in NSPCs in vitro and in vivo. Next, using a caspase-1 inhibitor (Ac-YVAD-CMK) to block caspase-1 activation in vitro and in vivo, we further demonstrated that X-ray irradiation may inhibit proliferation, induce senescence of NSPCs through caspase-1 activation. Together, our results suggest that caspase-1 activation is involved in irradiation-induced damage to NSPCs.